Optical device, optical scanning apparatus and image forming apparatus

Abstract

An optical device includes at least one surface emitting laser device having a dielectric film for causing a central portion of a light emitting region to have a comparatively higher reflectivity than a peripheral portion; a light receiving element disposed, with respect to a first direction, on one side to the surface emitting laser device; and a transparent member disposed in a path of light emitted from the surface emitting laser device and configured to reflect a portion of the light toward the light receiving element as monitoring light. The central portion has shape anisotropy in which a width measured on a line extending in the first direction and passing through the center of the light emitting region is smaller than a width measured on a line extending in a second direction, which is perpendicular to the first direction, and passing through the center of the light emitting region.

What is claimed is: 
     
       1. An optical device comprising:
 at least one surface emitting laser device having a transparent dielectric film for causing a central portion of a light emitting region to have a comparatively higher reflectivity than a peripheral portion of the light emitting region; 
 a light receiving element disposed, with respect to a first direction, on one side in relation to the surface emitting laser device; and 
 a transparent member disposed in a light path of light emitted from the surface emitting laser device and configured to reflect a portion of the light toward the light receiving element as monitoring light, 
 wherein the central portion has a shape anisotropy in which a width measured on a line extending in the first direction and passing through a center of the light emitting region is smaller than a width measured on a line extending in a second direction, which is perpendicular to the first direction, and passing through the center of the light emitting region. 
 
     
     
       2. The optical device as claimed in  claim 1 , wherein the peripheral portion of the light emitting region includes a first region and a second region opposing each other across the central portion, and a line connecting geometric centers of the first region and the second region is not perpendicular to a straight line formed by projecting, on a plane surface that includes the light emitting region, a normal line to the transparent member at an incident position of the light emitted from the surface emitting laser device. 
     
     
       3. The optical device as claimed in  claim 1 , wherein an incident angle of the monitoring light with respect to a light receiving surface of the light receiving element substantially coincides with a Brewster angle. 
     
     
       4. The optical device as claimed in  claim 1 , wherein the central portion is covered by the dielectric film which has an optical thickness of an even multiple of λ/4, wherein λ is an oscillation wavelength. 
     
     
       5. The optical device as claimed in  claim 1 , wherein the peripheral portion is covered by the dielectric film which has an optical thickness of an odd multiple of λ/4, wherein λ is an oscillation wavelength. 
     
     
       6. The optical device as claimed in  claim 1 , wherein the dielectric film is one of a silicon dioxide film and a silicon nitride film. 
     
     
       7. The optical device as claimed in  claim 1 , further comprising a package member having a region of space surrounded by walls, wherein the surface emitting laser device and the light receiving element are disposed on a bottom surface of the region of space, and the transparent member encloses the region of space. 
     
     
       8. The optical device as claimed in  claim 1 , further comprising plural of the surface emitting laser devices. 
     
     
       9. An optical scanning apparatus for emitting light onto a surface to be scanned, the optical scanning apparatus comprising:
 a light source having an optical device; 
 a deflector configured to deflect light emitted from the light source; and 
 a scanning optical system configured to focus the deflected light onto the surface to be scanned, 
 wherein the optical device includes
 at least one surface emitting laser device having a transparent dielectric film for causing a central portion of a light emitting region to have a comparatively higher reflectivity than a peripheral portion of the light emitting region; 
 a light receiving element disposed, with respect to a first direction, on one side in relation to the surface emitting laser device; and 
 a transparent member disposed in a light path of light emitted from the surface emitting laser device and configured to reflect a portion of the light toward the light receiving element as monitoring light, 
 
 wherein the central portion has a shape anisotropy in which a width measured on a line extending in the first direction and passing through a center of the light emitting region is smaller than a width measured on a line extending in a second direction, which is perpendicular to the first direction, and passing through the center of the light emitting region. 
 
     
     
       10. The optical scanning apparatus as claimed in  claim 9 , wherein the peripheral portion of the light emitting region includes a first region and a second region opposing each other across the central portion, and a line connecting geometric centers of the first region and the second region is not perpendicular to a straight line formed by projecting, on a plane surface that includes the light emitting region, a normal line to the transparent member at an incident position of the light emitted from the surface emitting laser device. 
     
     
       11. The optical scanning apparatus as claimed in  claim 9 , wherein an incident angle of the monitoring light with respect to a light receiving surface of the light receiving element substantially coincides with a Brewster angle. 
     
     
       12. The optical scanning apparatus as claimed in  claim 9 , wherein the central portion is covered by the dielectric film which has an optical thickness of an even multiple of λ/4, wherein λ is an oscillation wavelength. 
     
     
       13. The optical scanning apparatus as claimed in  claim 9 , wherein the peripheral portion is covered by the dielectric film which has an optical thickness of an odd multiple of λ/4, wherein λ is an oscillation wavelength. 
     
     
       14. The optical scanning apparatus as claimed in  claim 9 , wherein the dielectric film is one of a silicon dioxide film and a silicon nitride film. 
     
     
       15. The optical scanning apparatus as claimed in  claim 9 , wherein the optical device further includes a package member having a region of space surrounded by walls, wherein the surface emitting laser device and the light receiving element are disposed on a bottom surface of the region of space, and the transparent member encloses the region of space. 
     
     
       16. The optical scanning apparatus as claimed in  claim 9 , wherein the optical device includes plural of the surface emitting laser devices. 
     
     
       17. An image forming apparatus comprising:
 at least one image carrier; and 
 at least one optical scanning apparatus for emitting, onto the image carrier, light modulated based on image information, 
 wherein the optical scanning apparatus includes
 a light source having an optical device; 
 a deflector configured to deflect light emitted from the light source; and 
 a scanning optical system configured to focus the deflected light onto the image carrier, 
 
 wherein the optical device includes
 at least one surface emitting laser device having a transparent dielectric film for causing a central portion of a light emitting region to have a comparatively higher reflectivity than a peripheral portion of the light emitting region; 
 a light receiving element disposed, with respect to a first direction, on one side in relation to the surface emitting laser device; and 
 a transparent member disposed in a light path of light emitted from the surface emitting laser device and configured to reflect a portion of the light toward the light receiving element as monitoring light, 
 
 wherein the central portion has a shape anisotropy in which a width measured on a line extending in the first direction and passing through a center of the light emitting region is smaller than a width measured on a line extending in a second direction, which is perpendicular to the first direction, and passing through the center of the light emitting region. 
 
     
     
       18. The image forming apparatus as claimed in  claim 17 , wherein the image information is multi-color image information.